During the last two decades the problem of photoprotection of the skin has attracted increasing attention. It has become clear that exposure to sunlight may cause not only erythema photoallergy and photoagining of the skin but also can damage the cutaneous immune system and induce or increase the probability of malignant transformations. These dangers are probably reinforced by the lately observed decrease of stratospheric ozone levels causing an increase of UV radiation on the ground level. Because of these consideration as well as for commercial reasons the development and production of sunscreen formulations has become a field of ever increasing activity.
Many of the existing sunscreen formulations are based on the use of benzophenones and methoxycinnamic acid derivatives. Although these synthetic chemicals are effective UV-absorbers their protective action is relatively short. Being small organic molecules with molecular mass of <300 Da they partly penetrate into deeper regions of the epidermis where they may have adverse reactions such as suppressing the immune system of the skin. Some of them may have estrogenic effects.
These antisun or sunscreen compositions are commonly in the form of an emulsion of oil-in-water type (namely, a cosmetically acceptable support comprising a continuous aqueous dispersing phase and a discontinuous oily dispersed phase) which contains, in various concentrations, one or more conventional lipophilic and/or hydrophilic organic screening agents which are capable of selectively absorbing harmful UV radiation, these screening agents (and their amounts) being selected as a function of the desired protection factor (the protection factor (PF) being expressed mathematically by the ratio of the irradiation time required to reach the erythema-forming threshold with the UV screening agent to the time required to reach the erythema-forming threshold without UV screening agent).
Therefore, it will be highly advantageous to develop long-lasting nonpenetrating photoprotectors confined to the stratum corneum, based on natural products.